Home Forums Hunting & Shooting Ask The Gunwriters Bullet RPM Causing Bullet Failure

Isn't this the concept of bullet yawing which is tearing the bullet apart?

No.

And it's "yawing," not "yawning." Spell-check might have gotten you on that one...

Spell check did get me. Just fixed it. Thanks. I thought bullet yawing was about stability in flight as the bullet leaves the muzzle before it settles down. Essentially wobbling? This could tear it apart or no?

Yawing happens somewhat to any elongated (not round ball) bullet leaving the muzzle. It might have something to do with bullets coming apart, but in my experience the bullets that come apart most frequently have thin jackets and soft cores--and it happens more often in hot barrels and/or on warm days. They may even hit a relatively close-range target, and often leave a spray of molten lead around the bullet hole.

The barrel doesn't necessarily have to have a fast rifling twist, either. One of the more interesting examples occurred during a prairie dog shoot with Kimber years ago. We were all using a new .22-250 sporter they'd started making, which was actually designed as a coyote rifle instead of a PD gun--and was really too light for PD shooting.

But I also brought along my own Kimber .223 sporter, as a did a couple of other guys, and used it some, with the same brand of ammo loaded with the same bullet. It was a new factory load from a major company, designed to be inexpensive enough to shoot lots of varmints. It featured a relatively light hollow-point with a thin jacket and soft core.

We didn't start shooting until after lunch on a really hot day, and my friend Ron Spomer and I were shooting together. After maybe half an hour Ron started missing, and he's a fine shot. We thought the barrel might need cleaning, so did that--but the same thing happened afterward.

Finally we shot the rifle at a cardboard box about 50 yards away. You could see the lead-spray around his bullet holes within a few shots, as the barrel heated up after we'd paused to find the box and set it up. I shot my .223 at the box too, and never did have that problem, even after its barrel got hot, probably because the velocity was considerably lower. This was interesting partly because the .223 had the then-standard 1-12 twist, and the .22-250 had the then-standard 1-14 twist.

A couple other interesting things happened during that shoot. The rifle Ron used eventually got so hot the forend of the walnut stock caught on fire. It wasn't flaming, but smoke was pouring out of the forend alongside the barrel. Luckily, we had some big coolers along filled with ice and drinks, and the ice had melted enough for him to stick the entire barrel and forend under water--which put out the fire.

I had an interesting experience the second day. There were LOTS of prairie dogs, and since we were allowed to take the brass home I was putting each fired case in the daypack I brought along, to hold my cameras and other stuff. That morning I again started shooting the .22-250 I'd been assigned, but soon started missing. It was a cool morning, and the barrel was only getting warm, not hot--but as I kept shooting the missing became more frequent.

Eventually I realized the 22-250 was feeling more like a .375 H&H when it went off--and I was flinching. Now, a .22-250 sporter doesn't kick all that hard--but I'd shot it a LOT the previous afternoon and an hour or two that morning. I switched to the .223 and started hitting again--and after getting home with the brass found out I'd shot the .22-250 over 600 times before the flinch started...

Pitching/yawing happens when the spinning bullet is perturbed from it's original state by an externally applied torque, or a shift of the rotation axis. There are a few primary causes for this, such as asymmetric muzzle blast, aerodynamic jump, internal bullet imbalance, etc. Bullet imbalance, even a small one, is always a source of pitching/yawing as the bullet leaves the muzzle. When the bullet is traveling down the bor it is rotating around its center-of-form, even if the core inside is terribly imbalanced, but when it exits the muzzle it begins rotating around its center-of-mass, instead. This shift of rotation axis causes pitching and yawing. The de-stabilization of the bullet does not cause it to self-destruct, however.

A bullet coming apart is simply the result of the centripetal force produced by the bullet jacket not being able to match the centrifugal force produced by the rotational velocity of the bullet, and it tears apart.

Interesting. Did I read someplace that Kevin Robertson advocates slowing g the 375 H&H to 9.3x62 velocities due to.this yawing issue and claims better penetration and bullet performance? Maybe somewhere in The Perfect Shot Africa book?

I just got off the phone with Speer. Friendly people. Not surprising at all that they definitely were not surprised the bullet was coming apart out of a 1-7”. Said I needed to shoot 60 grains and up. Or slow this bullet down but thought I’d need to slow it down significantly. Believe I’ll just save them for my slower twist guns. No fault to Speer other than I hope they would print that info on their boxes. “Not for 1-7” twist barrels” who knows, they may work just fine out of 16” M4 guns.

Thank you all again for chiming in.

Todd

I’ve used a lot of that bullet in a 1/7 AR though mine are older production in the yellow and black plastic boxes. I’ve actually had good luck with the both accuracy and effectiveness wise. Mine only has an 18” barrel so maybe the lower velocity keeps them together.

To the OP ... it's a combination of rpm + barrel / throat roughness. I've had this situation develop over time in several rifles as the barrel "wears". The higher the RPM, the less rough a barrel has to be to cause the jackets to fail. The rougher a barrel gets, the lower the rpm will be where this starts to happen. Fouling makes it worse. You can often restore "things" temporarily with a really thorough cleaning.

Tom

https://en.wikipedia.org/wiki/Centripetal_force

I don't get it, but I don't think I need to.

I've always considered pitching and yawing to be a form of destabilization and plenty of folks here have told me how dumb and incorrect I am when I gave my 2 cents about bullets destabilizing in some situations.

I am getting the feeling now that many people here don't consider anything other than keyholing as being "destabilized" and that normal pitch and yaw happens when a bullet is still stabilized. I am putting 2 and 2 together now...

A couple of simple examples may help clarify.

When you are turning in circles in your car/truck, the centrifugal force that you experience is the force that pushes you toward the outside of the corner (away from the center of the circle). The centripetal force is applied by the car door/seat/seatbelt that pushes you toward the center of the circle and keeps you from flying across the truck.

When we were kids we used to play on the tire swing. We would spin in circles as fast as we could and see who could hold on the longest. Centrifugal force is what you experience when your body is being flung away from the center of the swing. Centripetal force is what your arms apply on the chains of the swing, pulling you into the center of the tire so your body doesn't go flying off the swing.

Similarly, centrifugal force is what is trying to fling the core and jacket away from the rotation axis of the bullet, and centripetal force is what the jacket applies toward the center of the bullet to hold everything together.

It's all in the definition of "stable". Of course, oscillation of the rotation axis is less stable than if the rotation axis were to remain fixed, but for the sake of categorizing stability, we need to define our terms. Typically we talk about gyroscopic stability as the ability of a spinning projectile to overcome an overturning force. This is why a bullet that is pitching and yawing (precessing) is still considered to be stable, as long as its rotation axis remains along the direction of travel (with some slight oscillation).

To your point, a bullet whose precession is quickly damped out entirely, or nearly so, is considered to be "super-stable".

Sometimes analogies and real-world examples that we have observed can help solidify physical principles. In football terms, the ball is still "stable" if a spiral was thrown, even if the spiral is wobbling a little bit. But as soon as the ball turns end-over-end, it has "destabilized". If the ball reaches a steady state after being thrown that we would call a perfect spiral with no wobble, it is "super-stable".

Thanks.

I have a 22-250 AI fast twist rifle that does that with most 55 grain bullets.

So far the only one that didn't blow apart was a second from SPS.

Bad thing is i have several thousand on hand and they were cheap,plus side it it shoots the heavy bullets real good.

Matchkings will reliably disintegrate just in front of the muzzle of my 1:4 .308 barrel when shot at normal velocity. They show improved BC and, most importantly improved SD of BC when shot at a velocity where they will survive (about 1600 fps).

In the same barrel, a robust bullet seems to have no issues. Typically it will also experience gains in BC and SD of BC. As a bonus, it can get a gain in terminal performance.

Why did I purchase a 1:4 .308 barrel? I thought 1:2 would be a bit extreme.

Hah, I love it!

Thanks for the data point. Your results are interesting, though not surprising.

I had a 6.5 cal barrel 'Melonite' treated in a batch of 4. The barrel had several rounds through it. It was exceptionally accurate. I had been shooting 130 grain Norma Diamonds through it. After the nitriding, it began throwing bullets out of the group. I would get 4 into .3 and a 5th bullet 12" away
Then i started getting bullets fail to reach the target. I can only guess the nitriding created a cutting tool out of the barrel. It would still shoot ballistic tips and a few others quite well.
My point is that some barrels are apparently harder on jackets than others

A rough throat can be very hard on bullets especially in a fast twist barrel